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Skyvisions
Skyvisions, ASE Certified Technician
Category: Toyota
Satisfied Customers: 14411
Experience:  Toyota Master Diagnostic
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Im getting erasable code p2238 that comes back within 1 min.

Customer Question

I'm getting erasable code p2238 that comes back within 1 min. I havd also gotten a p0031 on ocassion
Submitted: 6 years ago.
Category: Toyota
Expert:  Skyvisions replied 6 years ago.

Thank you for choosing JustAnswer and allowing me to help you resolve your Toyota questions!

 

When ever These codes are set in combination 90% of the time you are looking at a bad AFR sensor and this is fairly common on this truck. Without any live data stream info to monitor on a scan tool it is difficult to say for sure. This is B1S1.

 

Skyvisions

Customer: replied 6 years ago.
Is the AFR sensor the same as the MAF sensor. And what is B1S1?
Expert:  Skyvisions replied 6 years ago.

The AFR sensor is not the same as a MAF sensor. AFR is an acronym for air fuel ratio. The sensors are similar to an O2 sensor (oxygen sensor) but operate totally different and are not interchangeable. MAF is an acronym for mass airflow sensor which is located in the intake induction usually near the air cleaner box. B1 S1 is how the sensors are identified this is bank one sensor one. These codes that you had indicate a malfunction in the heater circuit of the sensor and the actual performance of the sensor itself.

 

Skyvisions

Customer: replied 6 years ago.
Thank you for clarifying. Does that mean the heater circuit is within the sensor itself and there is just a supply voltage for the heater circuit to work. Is that supply voltage the same source as the second O2/AFR sensor down by the cat. What is the voltage supposed to be at the 4 pin connecter? And as long as the wiring and connections are good, would it be a reasonable diagnosis then that if the second sensor sets no codes( assuming it's working fine and it's heater circuit is working) then the heater circuit within the one O2/AFR setting the code is faulty?
Expert:  Skyvisions replied 6 years ago.

Thank you for clarifying. Does that mean the heater circuit is within the sensor itself and there is just a supply voltage for the heater circuit to work.

 

This is correct the heater element is built-in to the AFR sensor itself and is energized with 12 V by way of the 20 amp EFI fuse and EFI main relay and the computer makes the ground for the windings or heater element and duty cycles this on and off. Normally the heater element itself is what goes bad but in some very rare cases I have seen it damage the driver in the computer. The same power supply provides voltage to the rear oxygen sensor for that heater element in it. If you have not had any codes for that rear O2 sensor or Bank one sensor two then you are not dealing with a power supply problem otherwise it would set the code for that also. If you are looking at just the wires on the oxygen sensor side of the connector the two black wires are the through wires for the element in the sensor. These are the two wires that can be OHM tested. That is the only OHM reading that you can take on an AFR sensor. If you have a live data list scan tool you can monitor the voltage of the AFR sensor and ideally it needs to be 3.3 V to equal to 14.7 to 1 air fuel ratio mixture. Which is the theoretical ideal air to fuel ratio.

 

Skyvisions

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Customer: replied 6 years ago.
Thank you Sir! The heater element was open. I compared it to the new one I have to install. Just out of curiosity, does the AFR sensor still work properly after the engine warms up?
Expert:  Skyvisions replied 6 years ago.

The AFR works all the time! Never stops. The heater portion is variable depending on engine temp.

 

Skyvisions

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